Embodiments disclosed herein relate to wireless communications, and more particularly to signaling for interference reduction.
3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) represents a project within the third generation partnership project, with an aim to improve the UMTS (Universal Mobile Telecommunications System) E-UTRA (Evolved Universal Terrestrial Radio Access) standard. The 3GPP LTE radio interface may provide relatively high peak data rates, relatively low delays, and/or an increase in spectral efficiencies. The LTE ecosystem supports both Frequency division duplex (FDD) and Time division duplex (TOD) to enable network operators to exploit both the paired and unpaired spectrum since LTE has flexibility in bandwidth by supporting 6 bandwidths 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz.
The LTE physical layer is designed to achieve higher data rates, and is facilitated by turbo coding/decoding, and higher order modulations (up to 64-QAM). The modulation and coding is adaptive, and depends on channel conditions. Orthogonal frequency division multiple access (OFDMA) is used for the downlink, while Single carrier frequency division multiple access (SC-FDMA) is used for the uplink. Such schemes may provide an advantage that the channel response is relatively flat over a sub-carrier even though the multi-path environment could be frequency selective over the entire bandwidth. This may reduce complexity involved in equalization, as simple single tap frequency domain equalizers can be used at the receiver. OFDMA may allow LTE to achieve relatively higher data rates, reduced latency, and/or improved capacity/coverage, with reduced cost to the network operator.
An LTE/LTE-A system may use frequency reuse equal to one, meaning that the neighbor cells use the same resources (in time and frequency). Performance of UEs in one cell may be impacted due to the transmission of data/reference/control channels in a neighbor cell. One method to improve performance of UEs subject to interference from a neighbor cell may include using Network Assisted Interference Cancellation (NAIC) signaling. For these reasons, a work item on NAIC is being developed in 3GPP for LTE.
The terms interference mitigation receiver, interference cancellation receiver, interference suppression receiver, interference rejection receiver, interference aware receiver, interference avoidance receiver, or any combination thereof are interchangeably used, and they all belong to a category of advanced/enhanced receivers. Interference cancellation or suppression by such advanced receiver structures can lead to the elimination/reduction of the interference, in which case the interference may be completely cancelled and/or substantially reduced, whereas in other cases, the impact of interference on the useful signal may be reduced. Examples of signals or channels whose interference may be mitigated include PDSCH, PDCCH, PCFICH, PBCH, etc.
FIG. 1 is a message sequence chart of a proposed NAIC signaling scheme currently being studied in 3GPP. The aggressor node (also referred to as an aggressor base station) is the node causing interference to UEs receiving signals from the victim node (also referred to as a victim base station), e.g., a serving node, neighboring node etc. For example, the UE receiving signals (e.g. perform measurements, etc.) from one neighboring node may receive interference from another neighboring node or even from the serving node. This node may be referred to as the victim node, and the UEs which are connected to this node (the victim node) may be referred to as victim UEs. The aggressor node may also be interchangeably referred to as an interfering node, an interfering source, and/or an interfering cell. As shown in FIG. 1, the aggressor node may send the assistance information (described later) to the victim node via any opportune and/or available interface, for example, using the X2 interface or other high speed link. The victim node then sends the assistance information to the victim UE through higher layer (e.g. RRC or Radio Resource Control) signaling. Once the victim UE receives this information, the victim UE can estimate the neighbor cell (aggressor cell) channels (pilot, control, data, etc.) and remove the interference from the received signal.
Currently, there are discussions in 3GPP regarding a type of assistance information (also referred to as assisting information, assistance data, NAIC information, etc.) the aggressor node should send to the victim node and what information should be signaled to the UE by the serving node. The assistance information may include cell ID and/or CRS-IC info, Power offsets, “used Transmission Modes (TM) in eNodeB”, and/or “Resource allocation and precoding granularity,” etc. The assistance information may also include MBSFN (Multicast-Broadcast Single Frequency Network) subframe configuration in aggressor node, resource blocks used, modulation and coding scheme, etc. CRS-IC information, for example, is information that can assist in canceling CRS interference from neighbor cells.
According to existing NAIC methodologies and assuming that signaling of NAIC information is transmitted from aggressor node (also referred to as an interferer or interfering node) to victim node, the aggressor node may need to convey the assistance information to the victim node so that the victim node may use this information to configure the victim UEs via higher layer signaling. The victim UEs may use this information to cancel and/or mitigate interference from the aggressor node and/or aggressor UEs (i.e., UEs served by the aggressor node and/or generating interference). However, this may require that a potentially substantial and/or frequent amount of information is sent from the aggressor node to the victim node. Transmission of this information may limit a capacity of the inter node signaling interface (e.g. over X2 interface), and/or transmission performance degradation may occur due to unexpected conditions on the interface backhaul, such as increase of delay and/or jitter. Once the information is received, the victim node may need to send higher layer signaling to one or more victim UEs (e.g., via RRC), which may require additional resources (e.g., time, frequency, power, etc.). If such signaling is frequent and/or large in size, it could limit air interface resources available for the traffic channels for its own cell.